1. Field of the Invention
The present invention relates generally to a device and method for building an underground barrier. More particularly, this invention is directed to constructing a containment barrier underneath and around a hazardous waste site or municipal landfill.
2. Background Art
It is often necessary to form a containment barrier around a hazardous waste site to stop or prevent the migration of contaminants into the nearby soil and water tables. The containment barrier must prevent the migration of contaminants both horizontally and vertically away from the waste site. Therefore, a properly constructed containment barrier may be compared to a huge bathtub, with the hazardous waste contained within four side walls and a generally horizontal floor.
A present method is to physically remove the hazardous waste and haul it to a permitted storage facility. However, such method is costly, impractical, and dangerous. Digging up sites with buried drums, radioactive dusts, or other airborne wastes may actually release the contaminants, spreading them into the atmosphere and through the soil.
In response, researchers at Halliburton Nus Environmental Corp. have developed an apparatus and method to place a containment barrier around a hazardous waste site, as shown in International Publication Nos. WO 94/19547 and WO 93/00483. The Halliburton system uses a row of high pressure jets to shoot a slurry into the soil surrounding a hazardous waste site, somewhat liquefying the surrounding soil. The slurry cuts a path through the soil as it intermixes with the liquefied soil. Gravity and/or mechanical means pull the row of high pressure jets through the mix of liquefied soil and slurry. The liquified soil and slurry then harden into a protective barrier.
Although the Halliburton system has promise for some applications, it has several shortcomings that limit its use. First, the use of hydraulic jets may introduce liquids that can further spread contaminants. Second, because the system uses the same slurry for both cutting and mixing, in many applications there may be an imbalance between the amount of slurry needed for cutting and the amount of slurry needed for hardening the soil. Third, the hydraulic jets may only work in sandy or soft soils and may not work in rocky or hard soils.
Fourth, in the Halliburton system, the slurry is not controlled as it is deposited. Since the slurry mixes with the liquefied soil, the strength of the barrier depends on the soil composition encountered. Too little slurry may be deposited where the soil is easily cut. Excess slurry may be deposited where the soil is difficult to cut. Weak spots will form in the containment barrier if the soil contains air cavities or mixed pockesuch weak spots is unpredictable. Those using the Halliburton system have no way of knowing when and where such weak spots will be.